From ffb0603929617f39d449e942abe96cdba36e7545 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Tue, 23 Jul 2024 16:54:51 +0900 Subject: [PATCH] Improve comments in slru.{c,h} about segment name format slru.h described incorrectly how SLRU segment names are formatted depending on the segment number and if long or short segment names are used. This commit closes the gap with a better description, fitting with the reality. Reported-by: Noah Misch Author: Aleksander Alekseev Discussion: https://postgr.es/m/20240626002747.dc.nmisch@google.com Backpatch-through: 17 --- src/backend/access/transam/slru.c | 15 +++++++++++++++ src/include/access/slru.h | 7 +++---- 2 files changed, 18 insertions(+), 4 deletions(-) diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c index 77b05cc0a7..248aa1a655 100644 --- a/src/backend/access/transam/slru.c +++ b/src/backend/access/transam/slru.c @@ -72,6 +72,21 @@ #include "storage/shmem.h" #include "utils/guc_hooks.h" +/* + * Converts segment number to the filename of the segment. + * + * "path" should point to a buffer at least MAXPGPATH characters long. + * + * If ctl->long_segment_names is true, segno can be in the range [0, 2^60-1]. + * The resulting file name is made of 15 characters, e.g. dir/123456789ABCDEF. + * + * If ctl->long_segment_names is false, segno can be in the range [0, 2^24-1]. + * The resulting file name is made of 4 to 6 characters, as of: + * + * dir/1234 for [0, 2^16-1] + * dir/12345 for [2^16, 2^20-1] + * dir/123456 for [2^20, 2^24-1] + */ static inline int SlruFileName(SlruCtl ctl, char *path, int64 segno) { diff --git a/src/include/access/slru.h b/src/include/access/slru.h index 8a8d191873..97e612cd10 100644 --- a/src/include/access/slru.h +++ b/src/include/access/slru.h @@ -134,10 +134,9 @@ typedef struct SlruCtlData bits16 bank_mask; /* - * If true, use long segment filenames formed from lower 48 bits of the - * segment number, e.g. pg_xact/000000001234. Otherwise, use short - * filenames formed from lower 16 bits of the segment number e.g. - * pg_xact/1234. + * If true, use long segment file names. Otherwise, use short file names. + * + * For details about the file name format, see SlruFileName(). */ bool long_segment_names;